U.S. Pat. No. 5,618,063 to Chang et al., the entire disclosure of which is hereby incorporated by reference, discloses a multicolor heat sensitive verification system which can be used to prevent unauthorized or fraudulent reproduction of documents which can be reproduced by a color copier, such as cash register receipts, checks, pharmaceutical prescriptions, sweepstakes tickets, and the like. The heat sensitive multicolor system can also be used to selectively highlight desired portions of shipping labels, ATM receipts, promotional coupons, cash register receipts by application of thermal printers.
One form of multicolored heat-sensitive document is prepared by applying one or more localized heat-sensitive coatings over a fully coated substrate which had been coated with a heat-sensitive chromogenic coating. Application of heat to such coatings, for example, by the heated stylus of a thermal printer, results in different colors where the heat has been applied. However, difficulties have been experienced with such multicolor heat-sensitive documents because the underlying color can still be seen through the color of the overlying, localized coating resulting in reduced image quality of the color of the overlying coating.